# Extra Credit Project: Coefficient of Friction

## Measure the coefficient of static friction between various substances

This project must be done by individuals.

Your job in this assignment is to measure the coefficient of static friction between surfaces of various types.

You can measure the coefficient of static friction between an object and the surface on which it rests by simply tilting the surface until the object begins to slip. Make sure that you understand the principles involved.

You must measure the coefficient of static friction between your textbook's cover and at least 6 different materials. Two of these materials must be

• another copy of the textbook
• a quarter
but the others are up to you. You should try to find at least one material with a coefficient of static friction mu < 0.10, and at least one with mu > 1.0. For each material, make three trials. Measure the angle to which you must tilt the textbook in order to cause the object to slip in each trial, and record all measurements. Average the angles for each object and use the average angle to calculate the coefficient of static friction.

Make a table which lists the materials and their coefficients of static friction. Discuss briefly the results -- do they make sense?

Be sure to draw a picture of your setup. Describe carefully each piece of equipment you use.